1. Field of the Invention
The present invention generally relates to an image formation apparatus that includes an auxiliary power supply, and especially relates to an image formation apparatus such as a copying machine and a printer based on electronic photography, which image formation apparatus uses a power equalization control technique so that a great amount of power is made available without exceeding the maximum capacity from a commercial power line by providing power from the auxiliary power supply to a direct-current load (DC load).
2. Description of the Related Art
As a fixing unit 10 of the image formation apparatus based on the electronic photography, a heating roller method is often used in view of its high-speed operation and safety. According to the heating roller method, a printing medium P (such as paper) is inserted into a nip that is formed by a heating roller heated by a halogen heater and a countering roller. The countering roller is rotatable, arranged countering the heating roller, and pressed to the heating roller. In this way, the printing medium P is pressed and heated.
The heating roller is made of a metal, and made to have a great thermal capacity. For this reason, it takes a long time, which time ranges from several minutes to tens of minutes, before the temperature of the heating roller reaches a temperature required for a fixing operation. Such temperature is called “fixing temperature” and is about 180° C. For this reason, the temperature of the heating roller is maintained at a predetermined temperature during a standby period wherein no printing operations are carried out. That is, energy is consumed during the standby period so that the image formation apparatus can be immediately used.
In recent years and continuing, energy-saving regulations are enacted from the rise of environmental protection consciousness in countries worldwide. In Japan, the Rational Use of Energy Law is revised and reinforced; and in the US, energy-saving programs, such as Energy Star and ZESM (Zero Energy Star Mode), are enacted. In order to attain power savings in response to these regulations and programs, it is desired that the energy consumption during the standby period be reduced; or more preferably, that no standby power be required.
However, according to conventional fixing apparatuses, if the power is shut down during the standby period, it takes a long time before the heating roller becomes operational, causing inconvenience to users. For this reason, a device that is capable of promptly raising the heating roller temperature is needed so that an energy-saving copying machine, and the like, can be realized. In this connection, ZESM, for example, requires 10 seconds or less for re-starting from the standby period.
Then, the heating roller is made thin so that the temperature rising time can be shortened. Thin heating rollers have been widely used by image formation apparatuses of middle to low-speed. However, they are not adequate for high-speed machines with a printing speed of 60 cpm (copies per minute) or greater. The reason is that a great number of sheets pass the nip per unit time, and the temperature of the heating roller quickly falls due to the small heat capacity of the thin heating roller.
Although some image formation apparatuses use a power supply of 200 V for obtaining greater power so that the temperature fall is avoided, it is necessary to install a 200 V power supply, which is not a good general purpose solution. Further, there are other image formation apparatuses that use two 100 V 15 A electric power lines; however, it is difficult to have two independent 15 A wall sockets nearby. As described above, the present situation is that the upper limit of power cannot be raised without overcoming difficulties, which increase in power is required in order to raise the temperature of the heating roller in a short time.
Then, Patent References 1 and 2 propose that one of a rechargeable battery and a capacitor be used as an auxiliary power supply so that the maximum available power may be increased, and so that the temperature can be raised in a short time.
According to the conventional auxiliary power supply method, a heating member includes two or more heating elements such as halogen heaters. The first of the heating elements, for example, a halogen heater of 100 V 1200 W is heated by a main power supply 2 (FIG. 1). The second of the heating elements, for example, a halogen heater of 50 V 500 W is heated by the auxiliary power supply.
According to the conventional practice as described above, the power is supplied to the first heating element from the main power supply, and power can be supplied to the second heating element from the auxiliary power supply. The auxiliary power supply, charged with a battery charger, supplies the power at a desired timing according to the available power and the status of the image formation apparatus. In this way, power greater than available only from the main power supply 2 can be supplied to the heating member for heating the heating roller.
With the configuration described above, the temperature of the heating member can be raised to a desired temperature in a short time by simultaneously using the main power supply and the auxiliary power supply, as compared with the case wherein only the main power supply is used. Further, since the auxiliary power supply is discharged as it provides the power, temperature rising becomes slow. Then, when the image formation apparatus hangs up (becomes inoperable), safe maintenance operations can be performed.
Further, a great amount of heat per unit time is consumed, for example, in the case of a high-speed machine, in the case of thick paper, and in the case of continuous fixing operations. Accordingly, maintaining the desired temperature only with the main power supply is difficult; however, with the auxiliary power supply, the problems can be solved. In this case, too, since the temperature rise is decreased as the capacitor is discharged, safe maintenance operations may be conducted should the image formation apparatus hang up (become inoperable), while offering the quick temperature rise.
[Patent reference 1] JPA H10-282821
[Patent reference 2] JPA 2000-315567